Zen and its relationship with Japanese Budo goes right back to 12 century Japan.
Zazen is at the heart of Zen Buddhist practice. Zazen (literally "seated meditation") is a meditative discipline practitioners perform to calm the body and the mind and experience insight into the nature of existence.
It was introduced to the Japanese Samurai to show them how to always "be in the present moment"
It is also at the neart of the Budokan mindset.
It is the cement that binds all Japanese Budo together, because everything depends on the mind.
Shikantaza (just sitting) is objectless meditation, in which the practitioner does not use any specific object of meditation, but uses the power developed in concentration, through conscious breathing, to remain completely aware of all phenomena that arise and pass in the present moment.
All that is needed is - somewhere to sit that is free from any distractions - something to sit on so that you are comfortable and something that will require you to focus your mind - such as conscious breathing.
And the only other thng you need is time -around 20-30 minutes a day.
It is easy to do and the benefits are amazing - so what's not to like about it?